sql-utilities/src/Strata.SqlTools.Snowflake/Breakdowns/DeleteBreakdown.cs

using System.Collections;
using System.Text;
using SqlServerDeleteBreakdown = Strata.SqlTools.Breakdowns.SqlServer.DeleteBreakdown;
using StatementParser = Strata.SqlTools.Statements.Snowflake.StatementParser;

namespace Strata.SqlTools.Breakdowns.Snowflake;

/// <summary>
/// Represents a DELETE SQL statement breakdown with FROM and WHERE clauses for Snowflake.
/// </summary>
public class DeleteBreakdown : SqlServerDeleteBreakdown
{
    private static readonly StatementParser SnowflakeParserInstance = new StatementParser();

    /// <summary>
    /// Initializes a new instance of the <see cref="DeleteBreakdown"/> class.
    /// </summary>
    public DeleteBreakdown() : base()
    {
    }

    /// <summary>
    /// Initializes a new instance of the <see cref="DeleteBreakdown"/> class.
    /// </summary>
    /// <param name="fromClause">The FROM clause.</param>
    /// <param name="whereClause">The WHERE clause.</param>
    /// <param name="isMicrosoftSql">If true, uses Microsoft T-SQL parsing rules. If false, uses Snowflake parsing rules. Defaults to false.</param>
    public DeleteBreakdown(string fromClause, string whereClause, bool isMicrosoftSql = false)
        : base()
    {
        var parser = isMicrosoftSql ? Parser : SnowflakeParserInstance;

        var cleanFrom = parser.ExtractSqlComments(fromClause, out var fromComments);
        FromClause.Clause = cleanFrom.Trim();
        FromClause.Comment = fromComments.Count > 0 ? string.Join(" ", fromComments) : null;

        var cleanWhere = parser.ExtractSqlComments(whereClause, out var whereComments);
        WhereClause.Clause = cleanWhere.Trim();
        WhereClause.Comment = whereComments.Count > 0 ? string.Join(" ", whereComments) : null;
    }

    /// <summary>
    /// Gets the SQL breakdown as a string for Snowflake.
    /// </summary>
    /// <returns>The DELETE SQL statement.</returns>
    protected override string GetSqlBreakdown()
    {
        var sb = new StringBuilder();

        // Snowflake DELETE syntax is simpler - no DELETE clause with alias
        sb.AppendLine("DELETE FROM ");
        sb.AppendLine($"     {FromClause.Clause}");

        if (IsUsingWhereClause)
        {
            sb.AppendLine("WHERE ");
            sb.AppendLine($"     {WhereClause.Clause}");
        }

        return sb.ToString();
    }

    #region Parse Methods

    /// <summary>
    /// Parses a Snowflake DELETE SQL statement into a DeleteBreakdown object.
    /// </summary>
    /// <param name="sql">The DELETE SQL statement to parse.</param>
    /// <param name="isMicrosoftSql">If true, uses Microsoft T-SQL parsing rules. If false, uses Snowflake parsing rules. Defaults to false.</param>
    /// <returns>A DeleteBreakdown object representing the parsed statement.</returns>
    /// <exception cref="ArgumentNullException">Thrown when sql is null or empty.</exception>
    /// <exception cref="FormatException">Thrown when the SQL statement cannot be parsed.</exception>
    public static DeleteBreakdown Parse(string sql, bool isMicrosoftSql = false)
    {
        if (string.IsNullOrWhiteSpace(sql))
        {
            throw new ArgumentNullException(nameof(sql), "SQL statement cannot be null or empty.");
        }

        if (!TryParse(sql, out var result, out var error, isMicrosoftSql))
        {
            throw new FormatException($"Failed to parse {(isMicrosoftSql ? "T-SQL" : "Snowflake SQL")} DELETE statement: {error}");
        }

        return result;
    }

    /// <summary>
    /// Attempts to parse a Snowflake DELETE SQL statement into a DeleteBreakdown object.
    /// </summary>
    /// <param name="sql">The DELETE SQL statement to parse.</param>
    /// <param name="result">When this method returns, contains the parsed DeleteBreakdown if successful, or null if parsing failed.</param>
    /// <param name="isMicrosoftSql">If true, uses Microsoft T-SQL parsing rules instead of Snowflake rules. Defaults to false.</param>
    /// <returns>true if the SQL was successfully parsed; otherwise, false.</returns>
    public static bool TryParse(string sql, out DeleteBreakdown result, bool isMicrosoftSql = false)
        => TryParse(sql, out result, out _, isMicrosoftSql);

    /// <summary>
    /// Attempts to parse a Snowflake DELETE SQL statement into a DeleteBreakdown object.
    /// Handles Snowflake-specific syntax.
    /// </summary>
    /// <param name="sql">The DELETE SQL statement to parse.</param>
    /// <param name="result">When this method returns, contains the parsed DeleteBreakdown if successful, or null if parsing failed.</param>
    /// <param name="errorMessage">When this method returns false, contains a message describing why parsing failed.</param>
    /// <param name="isMicrosoftSql">If true, uses Microsoft T-SQL parsing rules instead of Snowflake rules. Defaults to false.</param>
    /// <returns>true if the SQL was successfully parsed; otherwise, false.</returns>
    public static bool TryParse(string sql, out DeleteBreakdown result, out string errorMessage, bool isMicrosoftSql = false)
    {
        result = null!;
        errorMessage = null!;

        try
        {
            if (string.IsNullOrWhiteSpace(sql))
            {
                errorMessage = "SQL statement cannot be null or empty.";
                return false;
            }

            // If Microsoft SQL mode, delegate to base class
            if (isMicrosoftSql)
            {
                if (!SqlServerDeleteBreakdown.TryParse(sql, out var baseResult, out errorMessage))
                {
                    return false;
                }

                // Convert to Snowflake DeleteBreakdown
                result = new DeleteBreakdown
                {
                    FromClause = baseResult.FromClause,
                    WhereClause = baseResult.WhereClause,
                    DeleteClause = baseResult.DeleteClause,
                    SetupClauses = baseResult.SetupClauses,
                    FinishClauses = baseResult.FinishClauses
                };

                return true;
            }

            var parser = SnowflakeParserInstance;
            sql = parser.NormalizeSqlPreservingComments(sql);

            // Check if it's a DELETE statement
            var sqlTrimmed = sql.TrimStart();
            if (!System.Text.RegularExpressions.Regex.IsMatch(sqlTrimmed, @"^\s*DELETE\b",
                System.Text.RegularExpressions.RegexOptions.IgnoreCase, Strata.SqlTools.SqlBreakdown.Utilities.RegexDefaults.MatchTimeout))
            {
                errorMessage = "SQL statement must start with DELETE.";
                return false;
            }

            // Extract setup and finish clauses
            var setupClauses = new List<string>();
            sql = parser.ExtractSetupClauses(sql, setupClauses);

            var finishClauses = new ArrayList();
            sql = parser.ExtractFinishClauses(sql, finishClauses);

            // Snowflake uses simpler DELETE syntax: DELETE FROM table WHERE condition
            var deleteMatch = System.Text.RegularExpressions.Regex.Match(sql,
                @"DELETE\s+FROM\s+(.*?)(?:\s+WHERE\s+(.*))?$",
                System.Text.RegularExpressions.RegexOptions.IgnoreCase | System.Text.RegularExpressions.RegexOptions.Singleline, Strata.SqlTools.SqlBreakdown.Utilities.RegexDefaults.MatchTimeout);

            if (!deleteMatch.Success)
            {
                errorMessage = "Could not parse DELETE statement. Expected format: DELETE FROM table [WHERE condition]";
                return false;
            }

            var fromClause = deleteMatch.Groups[1].Value.Trim();
            var whereClause = deleteMatch.Groups.Count > 2 ? deleteMatch.Groups[2].Value.Trim() : string.Empty;

            result = new DeleteBreakdown(fromClause, whereClause, isMicrosoftSql: false)
            {
                SetupClauses = setupClauses,
                FinishClauses = finishClauses
            };

            return true;
        }
        catch (Exception ex)
        {
            errorMessage = $"Unexpected error during parsing: {ex.Message}";
            return false;
        }
    }

    #endregion
}